This invention relates generally to paper composite materials and, more particularly, to such materials having an ultra-high tear resistant plastic core. The composites of this invention can be laser printed and used both indoors and outside, inasmuch as the paper component does not absorb water.
Paper is a semi-synthetic material made using chemically processed cellulose fibers. The advantages of paper as a medium for written communication include its low cost and the fact that it can readily be printed and colored using standard inks. However, paper has several disadvantages, including low tear and burst strength. It is also highly moisture absorbent unless treated with a water resistant material.
One approach to absorbency concerns has been the use of plastic-coated cellulosic papers, of the type used for posters, signs and shipping tags, and other products demanding resistance to hard wear and to outdoor exposure. Unfortunately, such plastic-coated papers lack suitable tear and burst strength. Another approach has been to coat papers on one or both sides with a suspension of clays, starches, rosin or wax, or a combination of these substances. Again, tear and burst strength are less than optimal.
In recent years, paper-like products have been made using polymeric plastic sheetings, such as those materials commercially-available under the Tyvec trademark. These products not only have a tear and bursting strength far superior to paper, but they are also waterproof However, such plastics have low affinities for adhesives and, as a result, are unsuitable for use in many fabricated products. They are, likewise, not suitable for laser print applications.
As is often the situation, the functional requirements for a specific end use application cannot be fully met by a single material. The search for a practical approach to a multi-functional material has been a long-standing concern in the art. Recently, various laminated materials have been devised to address the multi-functional requirement. U.S. Pat. No. 5,244,702 describes one such material: an outer paper sheet is adhered to a reinforcing film of synthetic plastic. The laminant is described as having good tear and burst strength characteristics, and as readily printable using standard inks.
Nonetheless, the prior art has associated with it a number of significant problems and deficiencies. Most are related to incomplete functional utility and result from the materials utilized. For instance, the materials described in the aforementioned '702 patent are described as having a paper component which absorbs water. Such a characteristic would not lend itself as suitable for outdoor applications.
Likewise, the materials disclosed in the '702 patent are described as having a high affinity for standard printing inks. The same materials are also described as having a tensile strength, but this quality is seriously impaired upon application of heat to the plastic film component. Laser printers are becoming increasingly popular, and laser print inks are not the standard printing inks mentioned in the '702 patent. It would appear that laser inks are excluded from the technology described in the '702 patent. This position is supported by the fact that most standard plastic films, such as those described in the '702 patent, will soften, disform and even melt at the operating temperatures of most desktop laser printers. On the other hand, materials of the prior art which are able to withstand such temperatures are invariably those which provide neither outdoor durability nor the required tear resistance that many applications demand. For instance, various polyesters will withstand the laser operating temperatures, but will not provide the necessary tear resistance for products that are either die-cut or perforated.